July’s Tip of the Month – Oil on Oil

Each month we will give a tip on how to improve your results, sourced either from the literature or our own research.

The Oil on Oil

Many IVF labs use micro drops under oil for embryo production, to protect the media from osmotic change and reduce the degree of pH change when transitioning to-and-from the incubator environment. However, many embryologists would like to eliminate oil from their IVF systems; its messy and is a source of impurities that may negatively impact embryo development and quality. So why is oil the preferred option to protect the media from osmotic and pH changes, especially when using with microliter micro drops of media?

Mineral oil is unique in its properties, because its hydrophobic (‘excludes water’) nature but allows gas to exchange between atmosphere and media

Oil is virtually impermeable to water vapour and even under 38-39 degrees temperature, there is undetectable osmotic change over the culture peiod. Most plasticware used for IVF is either polystyrene or polycarbonate, and these are more porous to water vapour than mineral oil. This goes unnoticed, as the amount lost is related to the surface area, of which the largest is the media-oil interface. Surround media with nothing but plastic at a high surface-area to volume ratio will cause osmotic change over several days.

Silicon oil is also less hydrophobic and enables water vapour to be lost.

This hydrophobic property of mineral oil is combined with an impressive property for gas exchange. Although not as efficient as direct aqueous equilibration, gas exchange through mineral oil occurs readily, enabling sufficient gas exchange to maintain pH equilibria when using bicarbonate/CO2 buffering.

Contamination of oil is an issue. In particular, oil is susceptible to contamination by volatile organic compounds, hydroperoxides and other oil-breakdown contaminates, especially if not stored well over time. Oil is best stored in glass, especially if aliquotting from a freshly purchased batch. Testing to identify individual contaminants is difficult, but these can be the cause of either poor or variable results if using unscreened oils. We recommend IVF laboratories source oil either from human IVF media companies or purchase specific mouse embryo assay tested oil.

ART Lab Solutions can facilitate your MEA testing requirements for oils and other laboratory consumables and products if required.

For more information on this month’s tip, contact admin@artlabsolutions.com